The patient now went on to have surgery. 

Histology

This is a high-grade mixed oligoastrocytoma that shows necrosis; which at the time of this case was classified as glioblastoma with oligodendroglial component, although it might have a better prognosis than standard glioblastoma.

The previous material was reviewed and it shows low-grade oligodendroglioma.

Immunohistochemistry:
GFAP+, P53+ strongly, KI-67 high (over 25%)

Final diagnosis:  Glioblastoma with oligodendroglial component, WHO grade IV.

Note: Under the current (2016) WHO classification of CNS tumors, this tumor is not easily classified. If the original tumor was indeed an oligodendroglioma (IDH mutant, 1p19q co-deleted) then this is now an anaplastic oligodendroglioma and not a glioblastoma.

As molecular status is unavailable this is best thought of as an oligodendroglioma NOS progressing to an oligodendroglioma NOS grade 3.

It may, however, have been an astrocytoma or even a glioblastoma based on the 2021 WHO classification.